The present application relates to military and commercial cargo transport structures, such as cargo pallets and intermodal shipping containers. The disclosed structure is especially suited to a cargo pallet, particularly a cargo pallet that is used to restrain cargo on transport structures.
A cargo pallet is a flat transport structure that supports goods in a stable fashion while being lifted by a forklift, pallet jack, front loader, work saver, crane, or other jacking device. Goods or shipping containers are often placed on a pallet secured with strapping, stretch wrap or shrink wrap and shipped. Cargo pallets can be made of wood, plastic, metal, or other materials. Cargo pallets made from aluminum have an advantage in that the metal panels used to assemble the cargo pallet are lightweight and malleable. Decreasing the weight of the panel in a structure may allow for increased loading on the panel and assembled structure. Aluminum panels can be prefabricated in modular units and joined together on site when placed in service. Aluminum panels are also more easily transported than heavier metals or preformed concrete. Furthermore, aluminum panels may be employed in new structures, or the panels may be used to refurbish an aging structure.
Cargo pallets typically consist of several panel members that have been joined together at their vertical seam abutments by various welding, filling, or fastening methods. Welding the panel faying surfaces (abutments) typically provides for more rigidity and increased load distribution, whereas non-welded fasteners allow enhanced and semi or fully-independent movement as between modular panels under changing load conditions. For structures where welded joints are desired, the use of friction stir welding (“FSW”) techniques has developed as one possible method for joining the members.
Friction stir welding generally includes the application of a pin or probe to the surface of a joint or seam. The pin applies pressure and friction (typically by spinning) on the seam sufficient to cause the metal of the faying surface to plasticize. The pin may be separately heated, but typically is designed to cause the metal to plasticize purely as a result of pressure without the need for additional heat or electricity. The pin moves along the length of the faying surface, and the plasticized metals from adjoining members are effectively “stirred” and intermix in the void created by the pin movement, thereby creating a weld seam. Additional filler material is typically unneeded. Because the yield strength threshold for various metals are usually well known, the FSW tool and pin can be precisely calibrated to apply no more than the exact pressure needed to cause the metal to plasticize and weld. This precise calibration also means that the weld joint cools and hardens almost immediately after the pin has passed a point in the faying surface. This results in a relatively instant weld without the application of broader heat, which can cause unwanted deformations.
Military cargo pallets, such as the standardized U.S. military 463L Master Pallet, are usually constructed with a smooth aluminum alloy exterior and a balsa wood core. Attachment of cargo to such a conventional pallet is accomplished by attaching chains or nets to tie-down rings located on the perimeter of the pallet. For example, the 463L Master Pallet has 22 tie-down rings that run along its edge. In FIG. 1, a conventional cargo pallet 10 is shown. Similarly, to the 463L Master Pallet described above, the cargo pallet 10 includes tie-down rings 12 that extend along the perimeter of the pallet 10. The cargo pallet 10 contains an exterior of aluminum, with a balsa wood core. As FIG. 1 shows, attachment of cargo to this type of conventional pallet is limited to the perimeter of the pallet 10.
Another type of cargo pallet exists that is composed solely of aluminum, and eliminates the balsa wood core that is traditionally used in the 463L Master Pallet. Unlike cargo pallets that contain a wood core, these all-aluminum pallets may include external and separate anchoring mechanisms (e.g., anchoring rails that may include slots) that are bolted on the aluminum structural members, and therefore can provide more attachment options than the 463L Master Pallet. FIG. 2 illustrates one such cargo pallet. The cargo pallet 20, shown in FIG. 2, is composed solely of aluminum, and thus eliminates the balsa wood core. Although these all-aluminum pallets provide more attachment options for anchoring cargo or other structures positioned on the pallet, the attachment options require external devices that are typically connected to the pallet using rivets and bolts. For example, the D-ring anchors positioned on the edge of the pallet are connected to the pallet using a process that may include machining and drilling the pallet before fastening the anchor rings using bolts. The requirement to fasten the anchors to the pallet (e.g., using a bolt/rivet assembly) results in pallets that are often complicated, heavy and can be expensive to manufacture.
Accordingly, a need exists for a lightweight cargo pallet with varied attachment options that is easy to manufacture.